THE MYROSINASE GENE FAMILY IN ARABIDOPSIS-THALIANA - GENE ORGANIZATION, EXPRESSION AND EVOLUTION

Myrosinase (thioglucoside glucohydrolase, EC 3.2.3.1.)is in Brassicace ae species such as Brassica napus and Sinapis alba encoded by two diff erentially expressed gene families, MA and MB, consisting of about 4 a nd 10 genes, respectively. Southern blot analysis showed that Arabidop sis thaliana contains three myrosinase genes. These genes were isolate d from a genomic library and two of them, TGG1 and TGG2, were sequence d. They were found to be located in an inverted mode with their 3' end s 4.4 kb apart. Their organization was highly conserved with 12 exons and 11 short introns. Comparison of nucleotide sequences of TGG1 and T GG2 exons revealed an overall 75% similarity. In contrast, the overall nucleotide sequence similarity in introns was only 42%. In intron 1 t he unusual 5' splice border GC was used. Phylogenetic analyses using b oth distance matrix and parsimony programs suggested that the Arabidop sis genes could not be grouped with either MA or MB genes. Consequentl y, these two gene families arose only after Arabidopsis had diverged f rom the other Brassicaceae species. In situ hybridization experiments showed that TGG1 and TGG2 expressing cells are present in leaf, sepal, petal, and gynoecium. In developing seeds, a few cells reacting with the TGG1 probe, but not with the TGG2 probe, were found indicating a p artly different expression of these genes.